1. Field of Invention
The present invention relates to an energy-saving device for a memory circuit. More particularly, the present invention relates to an energy-saving device capable of turning off the power to the second sense amplifier inside a memory circuit immediately after data transmission.
2. Description of Related Art
FIG. 1 is a diagram showing a conventional memory circuit. As shown in FIG. 1, the memory circuit includes a first sense amplifier 10, a second sense amplifier 12 and an input/output buffer 14. The first sense amplifier 10 sends out two different types of signals NL and NDL to the second sense amplifier 12. After some data processing activities inside the second sense amplifier 12, the data are transmitted to the input/output buffer 14 for output.
The second sense amplifier 12 is triggered by a local sense amplifier enable (LSAE) signal acting through the gate terminals of the NMOS transistors 16, 18 and 20. Since the output terminal of an inverter 22 inside the input/output buffer 14 is connected to the input terminal of another inverter 24 and vice versa, signal transmitted to the input/output buffer 14 can be retained. Hence, the second sense amplifier 12 must remain active for a definite period before it can be shut off after data transmission has stopped. Because the second sense amplifier 12 includes a plurality of MOS transistors inside, considerable current flows inside the second sense amplifier 12 and hence energy consumption is high.
Although the setting of a delay chain to control the opening and shutting down of the sense amplifier has been proposed to save energy , such a method is constrained by the manufacturing process as well as temperature variations. Consequently, proper timing control of the sense amplifier is very difficult leading to extra power consumption or failures.